This invention relates to a method for making terminal pads on a semiconductor device. In the manufacture of semiconductor integrated circuits and transistors, an insulative layer is formed over the surface of the semiconductor and electrical connection is made between particular surface regions of the semiconductor device by aluminum film strips overlying the insulative layer and contacting the particular regions through holes provided therefor in the insulative layer.
It is often preferred to provide metal bumps on the pads and to make external connections by "face bonding" the device to a printed circuit. This may be achieved by the well known method of "flip chip" attachment that may be simply accomplished by reflow soldering. Aluminum presents serious difficulties in such bonding methods since it rapidly acquires an insulative oxide film over its exposed surfaces and is not directly solderable. For these reasons, one or more other metals such as zinc, nickel, copper and gold have been applied over the aluminum contact pads. Depositing of these other metals over the aluminum usually involves immersion and plating in a liquid bath containing an electrolyte.
For reasons heretofore not fully appreciated, the plated metal termination exhibits a high series resistance or in some cases presents an open circuit. These extreme conditions occur at only certain terminations on a given device and only some of the time.
It is therefore an object of this invention to overcome the above noted disadvantages of the prior art.
It is a further object of this invention to provide solderable terminals on a semiconductor device having uniformly thick aluminum under-layers with an over-layer of another metal.
It is yet a further object of this invention to provide high quality terminals that extend as solderable bumps from a face of the device.